Oxetane isomerization-polymerization

The stereoselective synthesis of unsaturated oxetanes has recently been achieved by Feigenbaum and coworkers.Previous studies have indicated that photochemical cis-trans isomerization of enals is rapid and results in the formation of equivalent amounts of stereoisomeric alkene adducts. " For example, irradiation of rran.r-crotonaldehyde and 2,6-dimethylfuran produced a 1 1 mixture of alkenic isomers (174) and (175) in 64% yield. Irradiation of 4-trimethylsilylbutyn-2-one and furan provided with S 1 stereoselectivity the bicyclic oxetane (176) in which the methyl group occupies the exo position, presumably because of the small steric requirement of the triple bond. Desilyation of the protected al-kyne produced an alkynic oxetane which was hydrogenated under Lindlar conditions to bicyclic vinyl-oxetane (177) attempts to use the unprotected butyn-2-one gave low isolated yields of oxetane because of extensive polymerization. The stereochemical outcome thus broadens previous alkynyloxetane syn-theses and makes possible the preparation of new oxetane structures that may be synthetically useful. 

Andrews and Feast d have described a further application of the Patemo-Buchi reaction in which furans are used in step-growth polymerization. Irradiation of m-dibenzoylbenzene and furan produced the monomeric 2 1 adduct (182), which was polymerized further with m-dibenzoylbenzene to produce polymers containing isomeric oxetane units. The step-growth polymerization in this case was limited by low monomer solubility, slow oxetane formation, and hydrogen abstraction processes that led to crosslinking. 

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